U.S. patent number 8,606,164 [Application Number 13/190,759] was granted by the patent office on 2013-12-10 for rotatable image heating member and image heating device.
This patent grant is currently assigned to Canon Kabushiki Kaisha. The grantee listed for this patent is Yusuke Jota, Akihito Kanamori, Eiji Uekawa. Invention is credited to Yusuke Jota, Akihito Kanamori, Eiji Uekawa.
United States Patent |
8,606,164 |
Uekawa , et al. |
December 10, 2013 |
Rotatable image heating member and image heating device
Abstract
An image heating device includes a rotatable image heating
member including an elastic layer and a surface layer in which a
filler is dispersed; and a fixed pressing member which is contacted
to a surface of the rotatable image heating member and forms a nip,
between itself and the rotatable image heating member, in which a
recording material for carrying an image is to be nip-conveyed. The
surface of the rotatable image heating member has a shape such that
projections are distributed by the filler so that a coefficient of
dynamic friction .mu.(hot) relative to said fixed pressing member
when a surface temperature of the rotatable image heating member is
a temperature during image heating and a coefficient of dynamic
friction .mu.(cold) relative to the fixed pressing member when the
surface temperature is a normal temperature satisfy,
.mu.(hot)<1.2.times..mu.(cold).
Inventors: |
Uekawa; Eiji (Susono,
JP), Kanamori; Akihito (Yokohama, JP),
Jota; Yusuke (Suntou-gun, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Uekawa; Eiji
Kanamori; Akihito
Jota; Yusuke |
Susono
Yokohama
Suntou-gun |
N/A
N/A
N/A |
JP
JP
JP |
|
|
Assignee: |
Canon Kabushiki Kaisha (Tokyo,
JP)
|
Family
ID: |
45526872 |
Appl.
No.: |
13/190,759 |
Filed: |
July 26, 2011 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20120027479 A1 |
Feb 2, 2012 |
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Foreign Application Priority Data
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Jul 28, 2010 [JP] |
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2010-169159 |
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Current U.S.
Class: |
399/330;
399/333 |
Current CPC
Class: |
G03G
15/2057 (20130101); G03G 15/2053 (20130101); G03G
15/2064 (20130101) |
Current International
Class: |
G03G
15/20 (20060101) |
Field of
Search: |
;399/330,333 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2003-091192 |
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Mar 2003 |
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JP |
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2007-328020 |
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Dec 2007 |
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JP |
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Primary Examiner: Laballe; Clayton E
Assistant Examiner: Sanghera; Jas
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper &
Scinto
Claims
What is claimed is:
1. An image heating device comprising: a rotatable image heating
member including an elastic layer and a surface layer in which a
filler is dispersed; and a fixed pressing member which is contacted
to a surface of said rotatable image heating member and forms a
nip, between itself and said rotatable image heating member, in
which a recording material for carrying an image is to be
nip-conveyed, wherein the surface of said rotatable image heating
member has a shape such that projections are distributed by the
filler so that a coefficient of dynamic friction, .mu.(hot), of the
surface of said rotatable image heating member when a surface
temperature of said rotatable image heating member is a temperature
during image heating and a coefficient of dynamic friction,
.mu.(cold), of the surface of said rotatable image heating member
when the surface temperature is 25.degree. C. satisfy,
.mu.(hot)<1.2.times..mu.(cold).
2. A device according to claim 1, wherein the filler has an average
particle size of 3 .mu.m or more and is 200% or less of a thickness
of the surface layer.
3. A device according to claim 1, wherein the filler includes a
plurality of types of fillers different in average particle
size.
4. A device according to claim 1, wherein the filler includes a
plurality of types of fillers including at least one species of a
nonspherical filler.
5. A device according to claim 1, wherein the surface layer is a
fluorine containing resin layer, and an addition amount of the
filler is 10 wt. % or more and 40 wt. % or less when a total solid
of the surface layer is 100 wt. %.
6. A device according to claim 1, wherein the surface layer is a
fluorine containing rubber latex layer, and an addition amount of
the filler is 10 wt. % or more and 60 wt. % or less when a total
solid of the surface layer is 100 wt. %.
7. A device according to claim 1, further comprising a heating
member for heating said rotatable image heating member from a
surface side thereof.
8. A rotatable image heating member for use with an image heating
device, comprising: an elastic layer; and a surface layer in which
a filler is dispersed, wherein the surface of said rotatable image
heating member has a shape such that projections are distributed by
the filer so that a coefficient of dynamic friction, .mu.(hot), of
the surface of said rotatable image heating member when a surface
temperature of said rotatable image heating member is a temperature
during image heating and a coefficient of dynamic friction,
.mu.(cold), of the surface said rotatable image heating member when
the surface temperature is 25.degree. C. satisfy,
.mu.(hot)<1.2.times..mu.(cold).
9. A member according to claim 8, wherein the filler has an average
particle size of 3 .mu.m or more and is 200% or less of a thickness
of the surface layer.
10. A member according to claim 8, wherein the filler includes a
plurality of types of fillers different in average particle
size.
11. A member according to claim 8, wherein the filler includes a
plurality of types of fillers including at least one species of a
nonspherical filler.
12. A member according to claim 8, wherein the surface layer is a
fluorine containing resin layer, and an addition amount of the
filler is 10 wt. % or more and 40 wt. % or less when a total solid
of the surface layer is 100 wt. %.
13. A member according to claim 8, wherein the surface layer is a
fluorine containing rubber latex layer, and an addition amount of
the filler is 10 wt. % or more and 60 wt. % or less when a total
solid of the surface layer is 100 wt. %.
14. A member according to claim 8, wherein said elastic layer
includes a low heat conductive layer and a high heat conductive
layer.
Description
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to a rotatable image heating member
for heating an image on a recording material and relates to an
image heating device.
As the image heating device, e.g., a fixing device for heat-fixing
an unfixed image on the recording material or a glossiness
increasing device (image modifying device) for increasing
glossiness of an image by heating the image fixed on the recording
material is used. The rotatable image heating member is a
roller-like or endless belt-like rotatable member, for heating the
image in contact with an image formed surface of the recording
material, by being externally or internally heated by a heating
means.
For example, as a heat-fixing device which is the image heating
device to be mounted in an image forming apparatus, such as a
copying machine or an LBP, in which an image forming process of an
electrophotographic type, an electrostatic recording type or the
like is employed, there have been known devices of various types
and constitutions.
One of the present inventors has proposed in Japanese Laid-Open
Patent Application (JP-A) 2007-328020, as a constitution of the
heat-fixing device simplified for the purpose of reduction in cost
and size, a device of a pressing member-fixed type. This device
uses a non-rotational fixing member such as a pressing pad or a
pressing sheet as a pressing member press-contacted to a fixing
roller as a rotatable image heating member to form a fixing nip in
which a recording material is to be nip-conveyed. Further, JP-A
2003-91192 discloses a fixing device in which a sheet-like pressing
member having a leaf spring property if contacted to the fixing
roller and recording paper (recording material) on which a toner
image is transferred is heated and pressed when being passed
between the fixing roller and the sheet-like pressing member, thus
fixing the toner image on the recording paper.
In such a heat-fixing device of the pressing member-fixed type, the
pressing member which is the non-rotational fixing member
constitutes a conveyance resistance of the recording material in
the nip. Therefore, for the surface of the pressing member, a
material having a small friction coefficient is selected, and for
the surface of the fixing roller, a material having a large
friction coefficient is selected. As a result, the recording
material is conveyed while slides on the surface of the pressing
member at its back surface. Specifically, for the surface of the
fixing roller, a material such as silicone rubber with a strong
tack property is used or a material for increasing a frictional
force is contained, as a filler, in fluorine-containing resin.
However, when a friction coefficient .mu. of the fixing roller
surface is high, the fixing roller surface and the pressing member
surface directly rub with each other, so that the frictional force
becomes very large. In order to rotate the fixing roller with the
large frictional force, a rotational torque is increased and
therefore a motor with a large output is required in order to
generate power therefor. Although the pressing member is fixed for
reducing the cost and the size, when the output of the motor is
increased, the cost is correspondingly increased and the size of
the motor is also increased, so that an intended purpose cannot be
achieved.
SUMMARY OF THE INVENTION
The present invention provides a further development of the
above-described conventional constitutions.
A principal object of the present invention is to provide a
rotatable image heating member capable of stably conveying a
recording material while suppressing a rotational torque by
suppressing a frictional force of a surface layer of the rotatable
image heating member of an image heating device of a pressing
member-fixed type against a pressing member.
Another object of the present invention is to provide the rotatable
image heating member capable of using a driving motor with a
smaller output by suppressing the frictional force of the surface
layer of the rotatable image heating member against the pressing
member to suppress the rotational torque.
A further object of the present invention is to provide the image
heating device of the pressing member-fixed type using the
rotatable image heating member capable of stably conveying the
recording material while suppressing the rotational torque by
suppressing the frictional force of the surface layer of the
rotatable image heating member against the pressing member.
A still further object of the present invention is to provide the
image heating device of the pressing member-fixed type capable of
using the driving motor with the small output to reduce cost and
size by suppressing the frictional force of the surface layer of
the rotatable image heating member against the pressing member to
suppress the rotational torque.
According to an aspect of the present invention, there is provide
an image heating device comprising:
a rotatable image heating member including an elastic layer and a
surface layer in which a filler is dispersed; and
a fixed pressing member which is contacted to a surface of the
rotatable image heating member and forms a nip, between itself and
the rotatable image heating member, in which a recording material
for carrying an image is to be nip-conveyed,
wherein the surface of the rotatable image heating member has a
shape such that projections are distributed by the filler so that a
coefficient of dynamic friction .mu.(hot) relative to said fixed
pressing member when a surface temperature of the rotatable image
heating member is a temperature during image heating and a
coefficient of dynamic friction .mu.(cold) relative to the fixed
pressing member when the surface temperature is a normal
temperature satisfy, .mu.(hot)<1.2.times..mu.(cold).
According to another aspect of the present invention, there is
provided a rotatable image heating member for use with an image
heating device, comprising:
an elastic layer;
a surface layer in which a filler is dispersed,
wherein the surface of the rotatable image heating member has a
shape such that projections are distributed by the filler so that a
coefficient of dynamic friction .mu.(hot) relative to said fixed
pressing member when a surface temperature of the rotatable image
heating member is a temperature during image heating and a
coefficient of dynamic friction .mu.(cold) relative to the fixed
pressing member when the surface temperature is a normal
temperature satisfy, .mu.(hot)<1.2.times..mu.(cold).
These and other objects, features and advantages of the present
invention will become more apparent upon a consideration of the
following description of the preferred embodiments of the present
invention taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Part (a) of FIG. 1 is a schematic structural view of an image
forming apparatus in Embodiment 1, and (b) of FIG. 1 is a schematic
structural view of a fixing device.
Part (a) of FIG. 2 is a schematic sectional view for illustrating a
surface layer of the fixing device, and (b) and (c) of FIG. 2 are
schematic sectional views each for illustrating the form of a
projection of a surface layer of the fixing roller.
Part (a) of FIG. 3 is a graph for illustrating a change in
coefficient of dynamic (kinetic) friction (dynamic friction
coefficient) when the surface of the fixing roller is increased in
temperature, and (b) of FIG. 3 is a schematic view for illustrating
a measuring method of the dynamic friction coefficient.
Parts (a), (b) and (c) of FIG. 4 are schematic sectional views for
illustrating an effect of the present invention.
Parts (a) and (b) of FIG. 5 are graphs for illustrating the effect
of the present invention.
Part (a) of FIG. 6 is a schematic view for illustrating the fixing
roller surface, and (b) of FIG. 6 is a schematic view for
illustrating a measuring method of a recording material conveying
force.
Part (a) of FIG. 7 is a schematic view for illustrating an effect
in Embodiment 3, and (b) of FIG. 7 is a schematic view for
illustrating an effect in Embodiment 4.
FIG. 8 is a schematic structural view of a fixing device of a
fixing belt type.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Embodiment 1
(1) Image Forming Apparatus
Part (a) of FIG. 1 is a schematic structural view of an example of
an image forming apparatus 100 in which an image heating device
according to the present invention is mounted as a fixing device
(first heat-fixing device). This apparatus is a laser beam printer
using an electrophotographic process of a transfer type. That is,
an image is formed on a sheet-like pressing member P on the basis
of an electric image signal inputted from a host device 200 such as
a host computer or a network image reader to a controller 101 of
the apparatus 100. The controller 101 transfers various pieces of
electrical information between the host device 200 and an operating
portion 102 of the apparatus 100. Further, controller 101 effect
centralized control of an image forming operation of the apparatus
100 in accordance with a predetermined contact program or look-up
table.
Inside the apparatus, a drum-like electrophotographic
photosensitive member 1 as an image bearing member (hereinafter
referred to as a drum) is provided. The drum 1 is prepared by
forming a layer of a photosensitive material such as an OPC,
amorphous Se or amorphous Si on a peripheral surface of a drum
(cylinder)-like substrate of aluminum, nickel or the like. The drum
1 is rotationally driven at a predetermined speed (process speed)
in the clockwise direction indicated by an arrow, so that the
surface of the drum 1 is uniformly charged to a predetermined
polarity and a predetermined potential by a charging roller 2 as a
charging device. Then, the charged surface of the drum 1 is
subjected to scanning exposure with a laser beam L, by a laser
scanner 3 as an image exposure device, which is ON/OFF-modulated
depending on the image information inputted from the host device
200 to the controller 101. As a result, an electrostatic latent
image corresponding to a scanning exposure pattern is formed on the
surface of the drum 1. The electrostatic latent image is
visualized, as a toner image, with a developer (toner) by a
developing device 4. As a developing method, a jumping developing
method, a two-component developing method, FEED developing method
or the like is used. In many cases, a combination of image exposure
and a reverse developing method is used.
The toner image formed on the drum 1 is successively transferred
onto the recording material P in a transfer nip T which is a
contact portion between the drum 1 and a transfer roller 5 as a
transfer device. Sheets of the recording material P are stacked and
accommodated in a feeding cassette 103 and are fed one by one by
driving a feeding roller 104 with predetermined control timing, and
the fed recording material P is passed through a conveying path 105
and is introduced into the nip T. Here, a leading end of the
recording material P is detected by a top sensor 8 provided close
to the conveying path 105 so that an image forming position of the
toner image on the drum 1 and a writing start position of a leading
end of the recording material P are coincide with each other in the
nip T, so that the recording material P is timed to writing start
of the image on the drum 1. To the roller 5, a transfer bias which
has an opposite polarity to a toner charge polarity and has a
predetermined potential is applied from a transfer bias voltage
source portion (not shown) during nip conveyance of the recording
material P in the nip T. As a result, the toner image on the drum 1
surface is successively transferred onto the surface of the
recording material P.
When the recording material P passes through the nip T, the
recording material P is separated from the surface of the drum 1
and passed through a conveying path 106 to be introduced into a
fixing device 6. Then the recording material P is heated and
pressed, so that an unfixed toner image is fixed as a fixed image
on the recording material P. The recording material P coming out of
the fixing device 6 is passed through a conveying path 107 and is
discharged as an image formed product on a discharge tray 108.
Further, the drum surface after the recording material P is
separated therefrom in the nip T is subjected to removal of a
deposited residual matter such as untransferred toner by a cleaning
device 7 and then is repetitively subjected to image formation. A
sheet discharge sensor 9 is provided in the fixing device 6 and
detects paper jam or the like when the recording material P causes
the paper jam or the like between the top sensor 8 and the fixing
device 6.
(2) Fixing Device 6
Part (b) of FIG. 1 is a schematic structural view of the fixing
device 6 in this embodiment. The fixing device 6 is an image
heating device of a pressing member-fixed type and an external
heating type. The fixing device 6 includes a fixing roller 10,
having an elastic layer, as a rotatable image heating member for
heating the image on the recording material P. Further, the fixing
device 6 includes a plate-like heater 15, as an external heating
means for externally heating the fixing roller 10, contacted to an
outer surface of the fixing roller 10 to form a heating nip H.
Further, the fixing device 6 includes a non-rotational pressing
member 20 (fixed type pressing member) which is fixed and is
contacted to the outer surface of the fixing roller 10 to form the
fixing nip N in which the recording material P is to be
nip-conveyed. In this embodiment, the heater 15 and the pressing
member 20 are disposed at 180-degree opposite positions while
sandwiching the fixing roller 10.
1) Fixing Roller 10
The roller 10 is a roller member including the core metal 11 and
includes a surface layer 14, of a fluorine-containing resin
component, having the outer surface at which the filler is
dispersed. At least one elastic layer, i.e., two layers 12 and 13
are formed in this embodiment between the core metal 11 and the
surface layer 14. In the roller 10 in this embodiment, outside the
core metal 11, a low heat conductive layer 12 formed with a low
heat conductive silicone rubber (elastic layer) is provided.
Further, outside the layer 12, a high heat conductive layer 13
formed in a thin film with a high heat conductive silicone rubber
(elastic layer) and a parting layer 14 as an outermost layer
(surface layer) are successively provided.
The low heat conductive elastic layer which is the low heat
conductive layer 12 is formed of a silicone rubber composition in
this embodiment. Specifically, the silicone rubber composition
prepared by mixing 0.1-200 wt. parts of a hollow filler of 500
.mu.m or less in average particle size into 100 wt. parts of a
thermosetting organopolysiloxane composition is heat-cured to form
the low heat conductive layer 12. Here, the hollow-filler includes
a gas portion in a cured product to lower the thermal conductivity
as in a sponge rubber and is formed with a microballoon material or
the like. As such a material, it is possible to use any material
such as glass balloon, silica balloon, carbon balloon, phenol
balloon, acrylonitrile balloon, vinylidene chloride balloon,
alumina balloon, zirconia balloon or Shirasu balloon. The low heat
conductive has the functions of lowering thermal capacity of the
entire elastic roller and insulating the heat from the heater 15
contacted to the roller 10 from the outside, to keep the roller
surface temperature at a high level. When the roller surface is
increased in temperature from a stand-by state (waiting state of
the fixing device) up to a fixable temperature, the presence of the
low heat conductive layer 12 increases a temperature rising speed,
so that it becomes possible to reduce a waiting time until the
rising of the heater 15.
The high heat conductive layer 13 is formed with a solid silicone
rubber (solid elastic layer which is not foamed) and in which high
heat conductive particles of metal oxides or ceramics such as
alumina, aluminum nitride, SiC and zinc oxide are added. In this
embodiment, alumina particles are used. The thermal conductivity of
the high heat conductive layer 13 may preferably be increased as
high as possible. In this embodiment, the high heat conductive
layer 13 having the thermal conductivity of 1.5 W/mK is used.
Further, with a large thickness of the high heat conductive layer
13, a heat accumulating effect is liable to be obtained. However,
when the thickness is excessively large, the thermal capacity
becomes large and therefore the roller temperature is not
increased, so that a fixing efficiency is rather impaired. Further,
the thickness of the high heat conductive layer 13. Further, the
thickness of the high heat conductive layer 13 may desirably be
changed depending on the conveying speed of the recording material
P. This is because the thicknesses of the layers between which the
heat is transferred vary depending on the conveying speed of the
recording material P. According to a result of calculation by the
present inventors, in the case where the conveying speed is slow,
the heat present from the surface to a deeper portion of the high
heat conductive layer contributes to the fixing. However, it has
been found that only the heat accumulated at a lesser depth portion
contributes to the fixing with a higher conveying speed. That is,
in the case where the conveying speed of the recording material P
is slow, the thickness of the high heat conductive layer 13 may be
relatively thin and in the case where the layer with the thickness
which is more than necessary is provided, the thermal capacity is
increased and rather impairs the fixing efficiency. In this
embodiment, the recording material conveying speed is about 130
mm/sec and an optimum thickness at this speed is about 150 .mu.m.
Further, an outer diameter of the roller 10 is 12 mm.
Here, the elastic layer of the roller 10 is, as described above,
not necessarily required to include the two layers of the low heat
conductive layer and the high heat conductive layer and it is also
possible to employ such a constitution that a single solid rubber
layer is provided in the case where there is no problem in terms of
the rising time of the heater 15 or the heating efficiency of the
recording material P. Further, there is also no problem even when a
plurality of layers (two or more layers) are provided.
The surface layer (parting layer) 14 is formed of a
fluorine-containing resin component in which the filler is
dispersed. A projection is distributed and formed at the surface of
the surface layer 14 in such a manner that at least a part of the
filler is exposed from the surface layer surface or the filler is
protruded. Further, with respect to a dynamic friction coefficient
.mu. of the surface of the surface layer 14, when the dynamic
friction coefficient .mu.(hot) at the time of increasing the
surface temperature of the surface layer 14 to the temperature at
which the image is to be heated and the dynamic friction
coefficient .mu.(cold) at a normal temperature satisfy the
relationship of: .mu.(hot)<1.2.times..mu.(cold). With respect to
the surface layer 14, detailed description will be made later in
(4).
2) Heater 15
The heater 15 is formed in a plate-like shape with the low thermal
capacity. The heater 15 includes an elongated substrate 15a such as
an insulating ceramic substrate of aluminum, aluminum nitride or
the like or a heat resistant resin substrate of polyimide, PPS, a
liquid crystal polymer or the like. On the surface of the substrate
15a, along a longitudinal direction, an energization heat
generating resistor layer 15b of Ag (silver)/Pd (paradium),
RuO.sub.2, Ta.sub.2N or the like is formed in the thickness of
about 10 .mu.m and the width of about 1-5 mm by screen printing or
the like. Further, on the substrate 15a, a protective layer 15c for
protecting the resistance layer 15b may be provided within a range
of not impairing the heat efficiency. The thickness of the
protective layer 15c may desirably be sufficiently thin to make the
surface property good. As the protective layer 15c, it would be
generally considered that a protective layer formed by glass
coating or the like is used but is would be also considered that a
fluorine-containing resin layer is used. As the material for the
fluorine-containing resin layer, it is possible to use
perfluoroalkoxy resin (PFA), polytetrafluoroethylene (PTFE),
tetrafluoroethylene-hexafluoropropylene resin (FEP) and
ethylene-tetrafluoroethylene resin (ETFE). Further,
polychlorotrifluoroethylene resin (CTFE), polyvinylidene fluoride
(PVDF) and the like may also be used. Further, it is also possible
to coat an imide-based layer of polyimide, polyamideimide or the
like in a single layer or in a mixed layer. Further, a dry coat
lubricant of graphite, diamond-like carbon (DLC), molybdenum
disulphide or the like may be used. Further, in the case where the
substrate 15a is formed of aluminum nitride or the like which has
good thermal conductivity, the energization heat generating
resistance layer 15b may also be formed at an opposite side from
the fixing roller 10 with respect to the substrate 15a.
A heat insulating stay holder 16 for holding the heater 15 is
formed of the heat resistant resin material of the liquid crystal
polymer, PPS, PEEK or the like. Further, the holder 16 is urged
against the roller 10 by an urging means (not shown) such as an
urging spring or the like, so that the surface of the heater 15 is
press-contacted to the roller surface. As a result, between the
heater 15 and the roller 10 surface, the heating nip H with a
predetermined width (with respect to the rotational direction of
the roller 10) in which the roller 10 is heated is formed. Further,
between the heater 15 and the roller 10, a heat resistant sheet or
the like (not shown) for protecting the heater surface or
preventing deposition of a contaminant may be interposed.
3) Pressing Member 20
In this embodiment, the recording material 20 is a pad-like member
(pressing pad). The pad 20 includes an elongated base material 21
extending in the longitudinal direction and a sliding layer 22
formed on the surface of the base material 21. The pad 20 is
disposed opposed to the heater 15 with respect to a radial
direction of the roller 10. Further, the longitudinal end portions
of the base material 21 are held by a device frame (not shown) and
the pad 20 is urged toward the roller 10 side by an urging spring
23 as a pressing means. By an urging force of the spring 23, the
sliding layer 22 on the base material 21 is contacted to the
surface of the roller 10 to deform the elastic layer 12, so that
the nip N with the predetermined width (with respect to the
rotational direction of the roller 19 is formed. The spring 23 has
a coil spring shape and is disposed at three positions in total
including positions in the neighborhood of the longitudinal end
portions and central portion. As a result, the pad 20 can be urged
against the roller 10 in a state in which bending is suppressed and
therefore the nip N can be formed substantially uniformly.
Incidentally, the pressure in this embodiment is 5 kgf in total
(estimated for the heat-fixing device for an A4-sized recording
material; 0.23 kgf/cm as the pressure per unit length). This value
is lower than the pressure set in the conventional heat-fixing
device of the host roller type or the film heating type. In this
embodiment, the pressing member is of the fixed type (stationary
type) and therefore it is desirable that the pressure is lowered as
small as possible and thus the torque during the rotation of the
roller 10 is decreased. Therefore, a proper range of the total
pressure is 2 kgf to 10 kgf (0.09 kgf/cm to 0.45 kgf/cm).
The material for the sliding layer 22 may preferably have a sliding
property such that the conveyance of the recording material P is
not hindered, a parting property such that the toner or the like
transferred from the recording material P is not deposited and an
anti-wearing property such that the sliding layer 22 is not abraded
by sliding with the recording material P. For that reason, as the
material for the sliding layer 22, e.g., the fluorine-containing
resin such as PTFE, FEP or PFA or other resins such as PAI
(polyamideimide) or PI (polyimide) is used. On the other hand, the
material for the base material 21 is not particularly limited so
long as the material is suitable for formation and arrangement of
the sliding layer 22. The material for the sliding layer 22 is also
not limited to the materials described above. The base material 21
and the sliding layer 22 may be integrally provided.
(3) Fixing Operation of Fixing Device 6
The roller 10 is rotatably supported, at the end portions of the
core metal 11, by the device frame (not shown) via bearing members.
Further, the roller 10 is rotationally driven at a predetermined
speed in the clockwise direction indicated by an arrow by driving a
driving gear, by a rotationally driving system (not shown),
provided at an end portion of the core metal 11. The roller 10 is
rotated while sliding on the heater 15 in the nip H and on the
pressing member 20 in the nip N. Further, a temperature controller
109 of the controller 101 turns on a triac element 110 as an
energization driving means, so that energization to the resistance
layer 15b from an AC power source 111 via an electrode portion (not
shown) provided at the longitudinal end portion of the substrate
15a of the heater 15 is started. The resistance layer 15b generates
heat by being supplied with electric energy, so that the heater 15
is increased in temperature. The temperature of the heater 15 is
detected by a temperature detecting means 17 such as a thermistor
provided on the other surface (back surface) of the substrate 15a.
Detected temperature information is inputted into the temperature
controller 109. The temperature controller 109 appropriately
controls a duty ratio, wave number or the like of a voltage applied
to the resistance layer 15b on the basis of the inputted detected
temperature information, so that the heater 15 is kept at a
predetermined temperature (target temperature). The roller 10 is
(externally) heated in the nip H by the heat of the heater 15 from
the outside, so that the roller surface is heated up to the
temperature at which the toner can be fixed.
In this state, the recording material P on which the unfixed toner
image t is formed is introduced into the nip N with the image
surface toward the roller 10 side, so that the back surface side of
the recording material P is contacted to the sliding layer 22 of
the pressing member 20 and is nip-conveyed in the nip N while being
slid on the surface of the sliding layer 22. During this
nip-conveying process, the unfixed toner image t on the recording
material P is fixed on the recording material surface as a fixed
image by heat of the roller 10 and pressure in the nip N. The
recording material P coming out of the nip N is separated from the
roller 10 and then is conveyed for discharge. As another
constitution of temperature control of the fixing device 6, the
surface temperature of the roller 10 may also be kept at the
predetermined temperature by controlling the energization to the
resistance layer 15b of the heater 15 on the basis of a detection
signal of the surface temperature of the roller 10 detected by the
temperature detecting means.
(4) Constitution of Surface Layer (Parting Layer) of Roller 10
The structure, which is the feature, of the surface layer 14 of the
roller 10 will be described below in detail. First, as the base
material used in the surface layer 14, there is a need to contain
the fluorine-containing resin component from the viewpoint of
prevention of offset of the toner and contamination with the toner.
For example, in addition to the fluorine-containing resin material
such as PFA or FEP, a fluorine-containing rubber and a latex rubber
containing the fluorine-containing resin such as PFA or FEP may be
used as a suitable material. These materials may be used singly or
in mixture of a plurality of materials as the base material.
Further, an electroconductive material such as carbon black or the
like is mixed into the base material, so that the surface layer can
also be used as an electroconductive coating layer.
A coating liquid is prepared by mixing and dispersing, in a paint
of the base material, an oxide filler of silica, alumina, zinc
oxide, titanium oxide or the like or an inorganic filler of silicon
carbide, boron nitride, aluminum nitride, silicon nitride or the
like. In this embodiment, in view of a dispersibility in the base
material paint or the like, alumina or silicon carbide was
principally used as the filler. The coating liquid in which the
filler is dispersed is uniformly applied onto the roller surface by
a method such as spray coating or dipping. After the coating, the
coated liquid is dried and then backed in an electric oven at about
300.degree. C. for about 15 min. to form a film.
Incidentally, when the filler is dispersed in the base material
paint, a predetermined surfactant or dispersant may be added. In
the application step, it is desirable that the coating liquid is
applied while being kept in a state in which the filler is
uniformly dispersed in the mixture point. Depending on an amount
and size of the filler, the mixture paint is required to be
continuously stirred by a stirrer or the like so as not to settle
in the paint.
Part (a) of FIG. 2 is a schematic sectional view of the surface
layer 14. There is a need that a filler 18 is dispersed in the
fluorine-containing resin as the base material and a part of the
filler 18 is protruded from the fluorine-containing resin surface.
With respect to the protrusion of the filler 18, the state is not
limited to the state as shown in (b) of FIG. 2 in which the surface
of the filler 18 itself is exposed from the fluorine-containing
resin surface 14 as it is. As shown in (c) of FIG. 2, a part or all
of the filler 18 is coated with the fluorine-containing resin 14 so
as to provide a protruded shape providing projections and recesses.
That is, the roller 10 has a surface layer, at its outer peripheral
surface, of the fluorine-containing resin component in which the
filler 18 is dispersed. Further, at least a part of the filler 18
is exposed from the surface of the surface layer 14 or the surface
is protruded by the filler 18, so that the filler 18 is distributed
at the surface of the surface layer 14 to form the projections.
That is, the projections formed by the exposed portion and
protruded portion of the filler 18 are required to be distributed
over the surface of the surface layer 14.
An optimum surface state for compatibly realizing a reduction in
rotational torque of the roller 10 and a stable recording material
conveying performance by the projections and recesses formed by the
filler 18 will be described more specifically. In the case where
the pad 20 which is the pressing member of the fixed type is used,
in a state in which the roller 10 is rotated and the recording
material P is not passed through the nip N, the roller 10 surface
and the pad 20 surface are directly contacted and slid on each
other, so that a frictional force of the sliding surface largely
influences on the rotational torque. As a period of the state in
which the roller 10 is rotated and the recording material P is not
passed through the nip N, the period of pre-rotation (during
pre-rotation operation) of the apparatus 100 until the recording
material P is introduced into the nip N and the period of sheet
intervals during continuous sheet passing may be included. Further,
the period of post-rotation (post-rotation operation) of the
apparatus 100 performed after a series of print operation steps may
also be included. In order to rotate the roller 10 under a large
frictional force, the rotational torque becomes high and therefore
a motor with a large output for generating power therefor is
required. Although the pressing member is fixed for reducing the
cost and the size, when the output of the motor is increased, the
cost is correspondingly increased, so that the motor size becomes
large and an intended object cannot be achieved. When the
frictional force can be suppressed to a low level, the torque is
reduced naturally. The frictional force is determined by the
dynamic friction coefficient .mu. of the surface of the roller 10
against the pressing member 20.
In the case where the fluorine-containing resin is used as the base
material for the surface layer 14 of the roller 10, the dynamic
friction coefficient .mu. of the surface of the roller 10 assumes
the following behavior depending on the temperature. As shown in
(a) of FIG. 3, in the cases of a) in which the filler 18 is not
added to the base material for the surface layer 14, the dynamic
friction coefficient .mu. is increased with surface temperature
rise of the roller 10. This is attributable to a change of
viscoelasticity of the fluorine-containing resin with temperature.
When the viscoelasticity is decreased by surface temperature rise,
the material is largely deformed when the force is applied from the
outside. Actually, an elastic force for cancelling the deformation
instantaneously acts on the material, so that a resistance force
generates at the contact portion to result in a frictional force.
That is, the roller 10 in which the filler 18 is not added into the
surface layer 14 is increased in torque with temperature rise in a
state in which the roller 10 is slid and rotated in direct contact
to the pad 20. Further, in this state, even when the recording
material (paper) P is introduced into the nip N, a force of the
roller 10 for feeding the recording material P cannot largely
overcome the resistance force exerted from the pad 20 on the
recording material P, so that the recording material cannot be
conveyed.
Here, measurement of the dynamic friction coefficient .mu. in the
case where the surface temperature of the roller 10 was changed was
performed by a method shown in (b) of FIG. 3. That is, a sliding
sheet 60 is sandwiched between the roller 10 for measurement and a
slidable pressing plate 61 which is molded with stainless steel,
aluminum or the like. The pressing plate 61 is pressed against the
roller 10 with predetermined pressure (e.g., 500 gf). The sliding
sheet 60 may be SUS sheet or may be prepared by coating the
fluorine-containing resin with a coating material or a tape
material corresponding to the surface material of the pad 20 in the
device 6 in (b) of FIG. 1. In this embodiment, the SUS sheet 60
surface-coated with a fluorine-containing resin (PTFE tape ("Scotch
5490", mfd. by 3M) was used. A force gage 30 is attached to an end
portion of the sheet 60 and measures a force F for retaining the
sheet 60 to be conveyed in a (leftward) direction indicated by an
arrow when the roller 10 is rotated. The measured value F is
divided by the pressure to be calculated as the dynamic friction
coefficient .mu.. Further, the surface of the roller 10 is heated
in a non-contact manner by a heat source such as a halogen heater
70 and then the dynamic friction coefficient .mu. when the surface
temperature of the roller 10 is increased may be measured depending
on the temperature.
Next, the case where the filler 18 is added to the surface layer 14
will be considered. Here, in the following description, the
addition amount of the filler 18 is represented by weight percent
(wt. %) which is a percentage of the filler 18 when the entire
solid content (total solid) contained in the surface layer 14 after
the film formation is 100 wt. %. Further, the particle size of the
filler 18 is an average particle size. The filler particle size is
measured by a laser diffractometry. A representative measuring
device for the laser diffractometry may, e.g., be "Microtrac HRA"
manufactured by Nikkaso Co., Ltd. When a particle size distribution
obtained by the measurement is represented by a cumulation
distribution, a particle size indicating a cumulative value of 50%
is referred to as a median diameter (D50), which is used as the
average particle size. The particle size distribution may also be
measured by, in addition to the above-described diffractometry, a
Coulter counter method or the like. The particle size distribution
obtained by the definitive laser diffractometry or the Coulter
counter method with respect to spherical and nonspherical particles
does not reflect a shape factor of the filler such as spherical or
nonspherical but is represented as a diameter of a spherical body
having the same volume as the particles. Strictly, the shape of a
needle-like (whisker) or flake-like filler is represented by an
aspect ratio or the like but in the following, the filler particle
size is described by using the average particle size.
As the filler 18, rounded particles of alumina of 4.0 .mu.m in
particle size were used. As shown by b) in (a) of FIG. 3, in the
case where the addition amount of the filler 18 is 5 wt. %, the
tendency that the dynamic friction coefficient .mu. is increased
with the surface temperature rise of the roller 10 is similar to
that in the case where there is no filler in a). This is because
projections and recesses are formed at the roller surface by the
addition of the filler but an adhesiveness between the surface of
the roller 10 and the surface of the pad 20 is good in small
addition amounts of the filler and therefore the frictional force
between the surface of the roller 10 increased in resistance force
by the lowering in viscoelasticity and the surface of the pad 20
closely contacted to the roller surface becomes large. In the case
where the recording material P is passed in such a surface state,
by the effect of the added filler 18, the conveying force is
stronger than that in the case where no filler is present but the
conveying force is still insufficient to continuously convey the
recording material P stably.
On the other hand, as shown by d) in (a) of FIG. 3, in the case of
the roller 10 in which the filler addition amount is 20 wt. %, the
dynamic friction coefficient .mu. in a normal temperature state is
somewhat increased but is not increased even when the surface
temperature of the roller 10 is increased and remains at a
substantially constant value. This is because even when the
viscoelasticity of the fluorine-containing resin surface is lowered
by the temperature rise as shown in (b) of FIG. 4, the presence of
a large amount of the projections of the filler 18 which are
interspersed can reduce a contact area between the surface of the
roller 10 and the surface of the pad 20 to suppress the increase in
frictional force That is, a rotational torque suppressing effect is
obtained. In such a surface state, the recording material P is
introduced into the nip N. Then, as shown in (c) of FIG. 4, the
projections of the filler 18 present in the large amount in the
interposed manner at the surface of the roller 10 firmly anchor to
the recesses and projections of the recording material P, so that
forces of the projections for pushing out the recording material P
in the rotational direction of the roller 10 are joined together.
The force exerted from the surface of the roller 10 on the
recording material P is sufficiently larger than the resistance
force exerted from the pad 20, so that stable recording material
conveyance can be performed.
As described above, in order to compatibly realize the reduction in
frictional force at the surface of the roller 10 and the
improvement in conveying performance of the recording material P,
there is a need to form many projections at the roller surface by
adding the filler 18 in a sufficient amount. Part (a) of FIG. 5
shows a change in dynamic friction coefficient .mu. (T=180.degree.
C.) of the surface of the roller 10 when the addition amount of the
filler 18 is increased at the roller 10 surface temperature of
180.degree. C. The temperature of 180.degree. C. is the temperature
(image heating temperature) of the surface (of the surface layer
14) of the roller 10 during the image fixing operation of the
fixing device 6. As shown in (a) of FIG. 5, the increase in dynamic
friction coefficient .mu. is suppressed from the filler 18 addition
amount of about 10 wt. % (or more). That is, it is understood that
the addition amount of about 10% or more is effective in
suppressing the increase in torque of the roller 10. Further, as is
apparent from Table 1 appearing hereinafter, from the addition
amount of about 10 wt. %, the conveying force of the recording
material P is also started to be stabilized simultaneously with the
torque suppression.
Here, the surface state for achieving a sufficient anchoring effect
of the recording material P while reducing the contact area between
the surface of the roller 10 and the pad 20 is important. When the
amount of the filler 18 added to the surface layer 14, the amount
of the projections provided by exposure or protrusion of the filler
18 is decreased but is increased by the addition of the filler 18
in a large amount. Part (a) of FIG. 6 is a schematic view of the
surface of the roller 10 when the surface of the roller 10 is
subjected to enlarged observation. Such an observation image is,
e.g., obtained by taking an enlarged surface photograph with a
magnification of 500-1000 by using an observation device such as a
scanning electron microscope (SEM) or an optical microscope. For
example, from the observation image, the projections of the filler
18 are selected to calculate the sum of projected areas thereof and
the calculated sum of projected areas is divided by the sum of
projected areas of the entire (whole) observation image, so that an
occupied ratio (%) can be obtained.
Part (b) of FIG. 5 shows the change in dynamic friction coefficient
obtained by replacing the addition amount of the filler 18 (the
abscissa in (a) of FIG. 5) with the occupied ratio of the
projections of the filler 18. From (b) of FIG. 5, it would be
considered that the increase in dynamic friction coefficient .mu.
can be suppressed when the occupied ratio of the projections of the
filler 18 is about 5% or more (corresponding to about 10 wt. % or
more of the filler addition amount).
Although details will be described later in a section of
Comparative experiment, when the type, shape and particle size of
the filler 18 are different, the addition amount of the filler 18
which is effective in compatibly realizing the reduction in torque
and the increase in recording material conveying performance is
also different. However, even in the case where the type, shape and
particle size of the filler 18 are different, when the sum of
projected areas of the filler 18 exceeds about 5% of that of the
entire surface by adjustment of the addition amount, it was
possible to confirm that the torque suppression and enhancement of
the recording material conveying performance were compatibly
realized.
Therefore, it is important that the surface property is controlled
so as to provide the projections with the occupied ratio of 5% or
more by the addition of the filler 18. However, when an observing
method of the surface of the roller 10, a recognizing standard of
the projections of the filler 18 and an observer are different, the
size and number of identified projections are different, so that it
cannot be concluded that the projections in the occupied ratio of
5% or more is uniquely effective. Therefore, the occupied ratio of
the projections is an index for describing the surface state.
Actually, at the time when the type, shape and particle size of the
filler 18 used are determined, the torque, the dynamic friction
coefficient .mu. and the conveying force of the recording material
P during the heating are measured. Further, it is important to
grasp the addition amount such that the increase in torque and
dynamic friction coefficient .mu. due to the surface temperature
rise of the roller 10 is not confirmed and a corresponding surface
state.
In other words, the state in which the increase in torque and
dynamic friction coefficient .mu. due to the surface temperature
rise of the roller 10 is confirmed refers to a state in which a
characteristic of the fluorine-containing resin as the base
material dominantly influences the surface characteristic of the
roller 10 and a characteristic of the filler 18 is not yet
exhibited. Therefore, a sufficient recording material conveying
force cannot be obtained. By increasing the addition amount of the
filler 18, the characteristics of the filler and the projections
formed by the filler become dominant, so that these characteristics
bring about the effects of the torque suppression and stable
recording material conveying force during the temperature rise.
Therefore, by grasping the change in dynamic friction coefficient
in the normal temperature state and temperature-increased state at
the surface of the roller 10, it is possible to judge whether the
surface characteristic of the roller 10 is dominant with respect to
the base material characteristic or the filler characteristic.
By the method as represented by that shown in (a) of FIG. 3
described above, the dynamic friction coefficient .mu. is measured
depending on the temperature of the roller 10. The dynamic friction
coefficient .mu. at the normal temperature (e.g., 25.degree. C.) is
taken as .mu.(cold). Further, the dynamic friction coefficient .mu.
when the surface temperature of the roller 10 is increased up to
180.degree. C. (temperature for image heating) is taken as
.mu.(hot). In order to suppress the torque, as shown in the graph
of (a) of FIG. 3, the filler 18 in a sufficient amount (filler
addition amount: 20 wt. %) may desirably be added so as to satisfy:
.mu.(hot)=.mu.(cold) or .mu.(hot)<.mu.(cold).
When the factor which dominates the surface characteristic of the
roller 10 is switched from the characteristic of the projections
for the base material to that for the filler 18, in some cases, the
relationship between .mu.(cold) and .mu.(hot) satisfy the above
relationships. Further, in some cases, .mu.(hot) is slightly larger
than .mu.(cold) to result in unstable value. The case where the
filler addition amount is 10 wt. % as shown by c) in (a) of FIG. 3
corresponds to the latter cases. This would be considered because
the surface characteristic is liable to slightly influenced
correspondingly to the increase in surface area due to expansion or
the like of the roller 10 by the heating. Further, that is
attributable to a fluctuation, in dynamic friction coefficient .mu.
with a certain range, due to dispersion non-uniformity of the
filler 18 with respect to a circumferential direction of the roller
10, run out of the roller 10 itself and variation of a shaft axis.
However, when the time of actual use of the roller 10 was taken
into consideration, the recording material P could be stably
conveyed by the effect of the projections of the filler 18, so that
the increase in torque could also be suppressed. This will be
described later in detail with reference to Table 1.
In consideration of these factors, when
.mu.(hot)<1.2.times..mu.(cold) is satisfied as a condition in
which the effect of the present invention can be achieved, the
surface characteristic of the roller 10 is dominantly influenced by
the filler 18 and the projections formed by the filler 18. As a
result, it is possible to realize the torque suppression and stable
recording material conveying force during the use. Further, the
dynamic friction coefficient .mu.(hot) during the temperature rise
of the roller 10 is not limited to that at 180.degree. C. but may
also be that at the temperature at which the heat-fixing is
effected. When abnormal temperature rise or the like at the end
portion of the belt 10 during continuous sheet passing is also
taken into consideration, there is no problem when the dynamic
friction coefficient .mu. is measured at about 150.degree. C. or
more.
Further, when the amount of the added filler 18 becomes excessively
large, a film-forming property of the surface layer 14 is lowered,
so that the surface can be cracked after baking and the surface
coating can be cracked by stress of sliding during the rotation of
the roller 10. For that reason, the addition amount is adjusted in
view of the type of the fluorine-containing resin material as the
balloon and compatibility depending on the type and shape of the
filler used.
Further, with respect to a relationship between the amount and size
(outer diameter: average particle size) of the added filler, when
the above-described protrusion of the filler 18 is taken into
consideration, there is a need to adjust the relationship depending
on the film thickness of the surface layer 14, i.e., the
application (coating) amount. That is, in the case of a thick film
thickness, by using a large filler 18, the filler 18 is liable to
be protruded even in a small amount but is, when a smaller filler
18 is used, less liable to be protruded from the base surface
unless the addition amount is increased. On the other hand, in the
case of a thin film thickness, even a relatively small filler 18
can be protruded from the base surface but when the filler 18 is
excessively large, a protrusion amount becomes excessively large,
so that the filler 18 is liable to be separated from the base
material during the use and it becomes difficult to achieve a
desired function. The coating film thickness is influenced by
factors such as the type of the fluorine-containing resin as the
base material and the viscosity and coating conditions (spray
amount and the number of coating, e.g., in spray coating) of the
coating liquid and therefore these factors are required to be
appropriately adjusted. Further, the shape of the filler 18 is also
a factor which influences the conveying property of the recording
material P and therefore there is a need to select an optimum shape
depending on the purpose.
(5) Comparative Experiment
On the basis of the above-described viewpoints, effects with
respect to the type of the base material and the amount, size and
shape of the added filler 18 are compared with those in the
conventional constitutions and will be described below.
I: Consideration of Addition Amount of Filler 18
A difference in effect depending on the addition amount of the
filler 18 was checked. In this comparative experiment,
perfluoroalkoxy resin (PFA) was used as the base resin material for
the surface layer 14. In the case where PFA is used as the base
material, the viscosity of the paint in which the filler 18 is
added is low and therefore the film thickness of about 10 .mu.m is
optimum for the surface layer in order to obtain the surface
property free from unevenness. The filler 18 used is rounded
alumina particles (average particle size: 4 .mu.m) of pulverization
type. In the case where the entire surface layer 14 after the film
formation is 100 wt. %, the coating liquid is prepared so that the
weight % of the filler 18 is 0 wt. % to 50 wt. % and then is coated
by spray coating, dried and subjected to a predetermined baking
step to form a film. As described above, the addition amount of the
filler 18 is represented as wt. % which is the occupied ratio
(percentage) of the filler when the whole solid contained in the
surface layer 14 after the film formation is taken as 100 wt. %.
Further, the outer diameter of the roller 10 was 12 mm, and as the
pressing member 20, a pad prepared by coating the aluminum metal
plate 21 with the sliding layer 22 of PTFE as the
fluorine-containing resin was used. The thus prepared roller 10 was
mounted in the fixing device 6 and was subjected to measurement of
the rotational torque on the roller shaft during the rotation and
the conveying force during the recording material conveyance. The
results are shown in Table 1.
TABLE-US-00001 TABLE 1 EMB. AA*.sup.2 Torque CF*.sup.4 PP*.sup.5
.mu. .mu. .mu.(180.degree. C.)/ NO.*.sup.1 (wt. %) (kgf cm) (kgf)
(%) (180.degree. C.) (25.degree. C.) .mu.(25.degree. C.) CE 1 0 2.1
<0.1 0 0.23 0.12 1.917 CE 2 5 2.0 0.1 3.0 0.25 0.13 1.923 EI-1
10 1.35 0.4 5.0 0.17 0.142 1.197 EI-2 11 1.3 0.4 6.0 0.16 0.145
1.103 EI-3 20 0.9 0.4 9.0 0.14 0.15 1.933 EI-4 30 0.8 0.45 12.5
0.13 0.15 0.867 EI-5 40 0.85 0.45 14.0 0.135 0.15 0.900 CE 3 50
UM*.sup.3 UM*.sup.3 18.5 0.13 0.15 0.867 *.sup.1"CE" represents
Comparative Embodiment and "E" represents Embodiment. *.sup.2"A4"
represents the addition amount. *.sup.3"UM" represents the data is
unmeasurable due to crack of the coating and a poor film forming
property. *.sup.4"CF" represents the conveying force. *.sup.5"PP"
represents a projection proportion.
The torque (kgfcm) in Table 1 may desirably be, when a balance with
the motor output of the fixing device 6 used in this embodiment is
taken into consideration, about 1 kgfcm. When the torque is
increased to about 2.0 kgfcm, the roller 10 cannot be rotated. When
the torque is 1.4 kgfcm or less, the roller 10 is rotatable by the
driving force of the motor. Further, the conveying force (kgf) is a
magnitude of a back tension required to stop conveyance of A4-sized
plain paper (recording material) when the recording material is
conveyed while being nipped in the nip N, and is measured by using
a force gage 30 as shown in (b) of FIG. 6. In this embodiment,
stable conveyance of the paper (recording material) becomes
unstable unless the conveying force is 0.3 kgf or more.
Incidentally, a criterion of judgment of the recording material
conveying force is not determined uniquely but a necessary value of
the conveying force varies by the influences of a pressing force
for the recording material P from the transfer portion upstream of
the heat-fixing portion with respect to the recording material
conveyance direction, the conveying force exerted on the sheet
discharge portion and other auxiliary conveying members. The
criterion of judgment of the recording material convey is
determined depending on the image forming apparatus.
According to the comparative experiment with the results shown in
Table 1, in order to obtain optimum torque and conveying force, the
addition amount of the filler 18 is required to be those in
Embodiments I-1 to I-5. When the film forming property is also
taken into consideration, it can be said that the addition amount
of 10 wt. % or more and 40 wt. % or less per the total weight of
the surface layer 14 is optimum.
Further, in Table 1, the occupied ratio of the sum of projected
areas of the projections of the filler 18 to that of the entire
surface is indicated as the projection proportion. In Comparative
Embodiment 2 in which a large torque value is measured, the
occupied ratio is 3.0% and in Embodiment I-1 in which the torque is
started to be suppressed, the occupied ratio is 5.0%. From this, it
can be said that the occupied ratio of the projections is required
to be set at about 5.0% or more by the addition of the filler 18 in
order to suppress the torque.
Further, when the dynamic friction coefficient .mu. at the roller
surface temperature of 180.degree. C. is compared, it is understood
that the torque is decreased with a decrease in dynamic friction
coefficient .mu. (data of the dynamic friction coefficient .mu. in
Table 1 correspond to those in the graph of FIG. 5). A ratio of the
dynamic friction coefficient .mu.(180.degree. C.) during the
temperature rise of the roller 10 to the dynamic friction
coefficient .mu. (25.degree. C.9 at the normal temperature is
.mu.(180.degree. C.)/.mu.(25.degree. C.)=1.197. In comparison of
the dynamic friction coefficient .mu., the dynamic friction
coefficient .mu. at 180.degree. C. (during temperature rise) is
somewhat higher than that at 25.degree. C. (normal temperature) but
during the use in which the recording material P is conveyed, it is
possible to compatibly realize the torque suppression and the
stable recording material conveying force. That is, the surface
state of the roller 10 in Embodiment I-1 can be said that the
surface characteristic of the roller 10 is started to be changed
from the characteristic of the fluorine-containing resin as the
base material to the characteristic of the projections provided by
the filler 18. That is, in the surface state in which the
characteristic of the projections by the filler 18 is dominant as
the surface characteristic, a relationship:
.mu.(hot)<1.2.times..mu.(cold) is satisfied.
II. Consideration of Particle Size of Filler 18
In the comparison in I described above, the influence of the
difference in addition amount was considered when the average
particle size of the added filler 18 was the same. In this
comparison, the influence in the case where the particles of the
filler 18 different in particle size are used will be considered.
The fluorine-containing resin used as the base material and the
coating film thickness are the same as those in I of (5).
Similarly, the material for the filler 18 and the shape of the
filler 18 are the same as those in I, i.e., the rounded alumina.
Particles of the filler 18 providing the same coating film
thickness of 10 .mu.m and having different average particle sizes
of 8 .mu.m, 15 .mu.m, 20 .mu.m and 25 .mu.m were added while
changing the addition amount to form coated surface layers 14 and
then the comparative experiment was conducted. The results are
shown in Table 2.
TABLE-US-00002 TABLE 2 EMB. TH*.sup.2 FI*.sup.3 AA*.sup.4 Torque
CF*.sup.5 PP*.sup.8 NO.*.sup.1 Base (.mu.m) (.mu.m) (wt. %) (kgf
cm) (kgf) (%) CE 4 PFA 10 8 5 1.7 0.2 4.0 E II-1 PFA 10 8 10 1.0
0.45 8.5 E II-2 PFA 10 8 20 0.85 0.5 11.5 E II-3 PFA 10 8 30 0.8
0.5 14.5 CE 5 PFA 10 8 40 UM1*.sup.6 UM1*.sup.6 -- CE 6 PFA 10 15 5
2.0 0.2 2.5 CE 7 PFA 10 15 10 1.8 0.4 3.5 E II-4 PFA 10 15 20 1.1
0.55 8.5 E II-5 PFA 10 15 30 1.0 0.60 11.0 CE 8 PFA 10 15 40
UM1*.sup.6 UM1*.sup.6 -- E II-6 PFA 10 20 20 1.2 0.6 8.0 E II-7 PFA
10 20 30 1.1 0.65 10.5 CE 9 PFA 10 25 20 UM2*.sup.7 UM2*.sup.7 --
*.sup.1"CE" represents Comparative Embodiment and "E" represents
Embodiment. *.sup.2"TH" represents the film thickness. *.sup.3"FI"
represents the rounded alumina filler having the indicated average
particle size. *.sup.4"AA" represents the addition amount.
*.sup.5"CF" represents the conveying force. *.sup.6"UM1" represents
that the data is unmeasurable due to crack of the coating and a
poor film forming property. *.sup.7"UM2" represents that the data
is unmeasurable since the filler is liable to be separated.
*.sup.8"PP" represents the projection proportion.
For example. in the case where the particle size of the filler 18
is 8 .mu.m (Embodiment II-1 to II-3 in Table 2), even when the
addition amount of the filler 18 is the same, there is a tendency
that the torque is low compared with the case of the particle size
of 4.mu. (Table 1). This means that the particle size is increased
and even in a small addition amount, the filler is started to be
protruded from the coating film surface. This can also be
understood from the fact that the occupied ratio for the filler of
8 .mu.m in particle size is larger than those for other fillers
when the projection proportions of the fillers 18 in Table 2 are
compared. For the same reason, there is a tendency that the
recording material conveying force is somewhat increased. On the
other hand, there is a tendency that the film forming property when
the addition amount is increased becomes poor. The crack of the
coating film starts to occur from the addition amount of about 40
wt. %. Therefore, in the case where the particle size is changed
from 4 .mu.m to o8 .mu.m, an optimum addition amount is 10-30 wt.
%.
Next, in the case where the filler 18 of 15.mu. in particle size
larger than the film thickness of 10 .mu.m (Embodiment II-4 and
II-5), even when the filler addition amount is 10 wt. %, the
decrease in torque is not caused. This means that a dispersion
proportion of the filler with respect to the surface area is
decreased due to the increase in filler diameter. That is, a site
at which the filler itself is present is decreased and thus the
occupied ratio of the projections of the filler 18 per the
projected area of the entire surface is decreased to 3.5%. A smooth
PFA surface is increased between the sites, so that the sliding
area of the roller 10 with the pad 20 is increased and therefore
the torque cannot be suppressed. The torque suppression and the
conveying force increase can be expected by increasing the addition
amount but there is the same tendency as in the case of the filler
of 8 .mu.m in particle size that the film forming property is
impaired when the filler is excessively added. Therefore, when the
filler 18 having the outer diameter (average particle size) larger
than the film thickness is used, it is understood that the range of
the addition amount in which the effect can be achieved is narrowed
and the optimum addition amount is 20-30 wt. %. Further, although
the data of the dynamic friction coefficient is omitted in Table 2,
in a state in which the torque is effectively suppressed, the
dynamic friction coefficient .mu. during the roller surface
temperature rise was substantially equal to or less than that at
the normal temperature.
Further, even in the case where the filler having a further large
particle size of 20 .mu.m is used, the compatible realization of
the torque suppression and the recording material conveying force
increase can be maintained in the filler addition amount of 20-30
wt. %. However, in the case where the filler having a still further
large particle size of 25 .mu.m is used, the filler 18 is liable to
be separated from the coating film surface when the roller 10 is
actually used, so that a desired effect cannot be achieved at a
relatively early stage of continuous use. For that reason, the use
of the filler having an excessively large particle size is
undesirable.
From the above, in order to compatibly realize the torque
suppression and the recording material conveying force increase,
the optimum range is present depending on the film thickness of the
surface layer 14 and it would be considered that the upper limit of
the particle size of a usable filler is until about 200% of the
film thickness.
On the other hand, with respect to the lower limit of the filler
particle size with which the effect can be expected, e.g., as the
filler having the particle size smaller than 4 .mu.m for the filler
used in the comparison of Table 1, the rounded fillers of 3 .mu.m
and 2.mu. in particle size were used for the adjustment of the
addition amount. In both cases, the amount of the projections of
the filler 18 was increased with an increase in addition amount,
the effect of lowering the torque could be obtained. With respect
to the recording material conveying force, when the filler of 3
.mu.m is particle size is used, the conveying force of 0.32 kgf is
obtained in the filler addition amount of 30 wt. %, so that the
recording material can be conveyed. However, even when the filler
addition amount is increased, with respect to the filler of 2 .mu.m
in particle size, the conveying force of 0.26 kgf is merely
obtained, so that it was impossible to perform the stable recording
material conveyance. This is because the filler particle size is
excessively small and therefore the projections with a size
sufficient to provide a necessary recording material conveying
force cannot be formed. A similar result was also obtained with
respect to particles of the filler 18 having different shapes
described later.
As described above, the range of the average particle size of the
filler 18 capable of achieving the effect of the present invention
is 3 .mu.m (lower limit) or more and 200% (upper limit) or less of
the film thickness of the surface layer 14. Further, by using the
filler 18 having a larger particle size within this range, an
improvement in recording material conveying force is liable to
expected and it is possible to obtain a stable recording material
conveying property. Further, it was also found that the optimum
filler addition amount varies depending on the particle size of the
filler 18 used and these values are determined in consideration of
the point at which the torque decrease and the necessary recording
material conveying force can be compatibly realized and the limit
of film formation.
The optimum addition amount of the filler 18 is determined from the
preparation condition in this embodiment and therefore should be
appropriately adjusted in the case where the film forming property
is changed by changing the material used, the preparation condition
of the coating liquid or the baking condition. That is, the filler
addition amount is adjusted so as to be 10 wt. % or more and 40 wt.
% or less in the case where the total solid is 100 wt. % and is
also adjusted depending on the film thickness of the surface layer
14 and the average particle size of the filler 18.
III. Consideration of Shape of Filler 18
The influence of the shape of the filler will be described. With
respect to the alumina filler having the rounded shape used in II,
the effect was compared by using a spherical filler, a cubic
(rectangular) pulverization filler and a flake-like filler. All the
particles of the fillers have the average particle size of 8 .mu.m
and are added in the fixed addition amount of 20 wt. %. The base
material and the film forming condition are the same as those in I
and II.
The results are shown in Table 3,
TABLE-US-00003 TABLE 3 EMB. TH*.sup.2 FI*.sup.3 AA*.sup.4 Torque
CF*.sup.5 NO.*.sup.1 Base (.mu.m) (type) (wt. %) (kgf cm) (kgf) E
II-2 PFA 10 A 20 0.85 0.5 E III-1 PFA 10 B 20 0.8 0.35 E III-2 PFA
10 C 20 0.85 0.55 E III-3 PFA 10 D 20 0.9 0.6 *.sup.1"CE"
represents Comparative Embodiment and "E" represents Embodiment.
*.sup.2"TH" represents the film thickness. *.sup.3"FI" represents
the filler. "A" is the rounded alumina filler of 8 .mu.m in
particle size. "B is the spherical alumina filler of 8 .mu.m in
particle size. "C" is the cubic filler of 8 .mu.m in particle size.
"D" is the flake-like alumina filler of 8 .mu.m in particle size.
*.sup.4"AA" represents the addition amount. *.sup.5"CF" represents
the conveying force.
As apparent from the Table 3, there is a tendency that the
conveying force becomes small with the shape closer to the sphere
and is increased with the different shape (nonspherical shape).
When the filler shape is more different from the spherical, the
amount of the projections protruded (projected) from the base
surface of the surface layer 14 is liable to be increased and a
degree of anchoring to the paper fiber due to the filler shape is
increased and therefore it would be considered that the conveying
force is increased by the increase in anchoring effect on the
recording material P. With respect to the spherical filler 18, it
would be considered that the amount of coating of the filler
surface with the base material is large even when the filler is
protruded from the base surface during the coating, and therefore
the conveying force is weak since the roller is liable to be slid
even when the roller slides on the recording material P.
When the comparison results described in I, II and III are totally
considered, the particle size of the filler 18 may desirably be 3
.mu.m or more and 200% or less of the film thickness of the surface
layer 14. With respect to the filler shape, by using the
different-shaped filler (nonspherical filler of the plate like, a
needle (whisker) like, rectangular, cubic like, etc.) is used and
by adjusting the addition amount in the range in which the film
forming property is good, the torque decrease and the recording
material conveying force improvement can be compatibly realized
effectively. Here, it would be considered that a degree of
achievement of the film forming property and the effect is changed
depending on the base material used for the surface layer 14, a
treating condition of the coating liquid after the filler
dispersion, the coating, baking and drying conditions during the
preparation of the surface layer 14, treatment of the primer layer
provided between the surface layer 14 and the lower layer, and the
like. Depending on these conditions and constitutions, the filler
addition amount, shape and the like should be appropriately
optimized.
As described above, even in the case where the surface of the
roller 10 is increased in temperature by heating or the like, when
the increase in dynamic friction coefficient .mu.(hot) is
suppressed in the state in which the projections of the filler 18
are distributed over the surface, the following effects can be
obtained. That is, the projections and recesses distributed over
the roller surface from the surface state to the extent that the
contact area with the fixed type pressing member is decreased, with
the result that the frictional force is decreased and thus the
increase in torque can be suppressed. In addition, when the
recording material is passed, the projections of the protruded
filler sufficiently anchors to the recording material surface, so
that it becomes possible to provide a stable paper (recording
material) conveying force.
Embodiment 2
The constitutions of the image forming apparatus and heat-fixing
device used in this embodiment are the same as those in Embodiment
1 and therefore will be omitted from the description. This
embodiment is characterized by using, as the fluorine-containing
resin component (base material) for the surface layer 14, a
latex-type paint including a mixture of the fluorine-containing
resin and a fluorine-containing rubber. Herein, the coating in
which the fluorine-containing resin is dispersed in the
fluorine-containing rubber is referred to as a fluorine-containing
rubber latex coating unless otherwise specified.
As in Embodiment 1, in the case where the paint of the
fluorine-containing resin alone is used as the base material, the
(upper) limit of the film thickness of the coating capable of being
formed in the film is generally about 15 .mu.m. As described in
Embodiment 1, the limit of the average particle size of the added
filler depends on the film thickness and when the particle size is
excessively increased, the filler is liable to be separated, so
that such a problem that the surface property becomes coarse
occurs. Therefore, in the case of the fluorine-containing
resin-based material, the limit of the particle size of the usable
filler is about 20-30 .mu.m. Further, the addition amount in which
the filler can be dispersed is about 30-40 wt. %, so that it is
difficult to disperse the filler in a large amount.
On the other hand, it is difficult to form the film of the
fluorine-containing rubber latex of 10 .mu.m or less in film
thickness and from the viewpoints of the viscosity and specific
gravity of the coating liquid, the coating film thickness of about
20 .mu.m to about 30 .mu.m can easily be controlled in
manufacturing. The increase in coating film thickness means that
the particle size of the added filler can be increased. Further, by
incorporating the fluorine-containing rubber component, the coating
layer after the film formation has flexibility compared with the
case of the fluorine-containing resin alone and therefore the crack
due to the baking is also less liable to occur, so that it is easy
to add the filler in a larger amount. That is, by using the
fluorine-containing rubber latex coating as the base material for
the surface layer 14, it becomes possible to extend the range of
choices of the type and addition amount of the filler 18 to be
added in the surface layer 14.
IV: Consideration of Difference in Base Material
A behavior in the case where the fluorine-containing rubber latex
coating is used as the base material will be described with respect
to the effect while be compared with that in Embodiment 1.
The fluorine-containing rubber latex coating specifically used as
the base material for the surface layer 14 in this embodiment is a
fluorine-containing rubber latex ("GLS213F", mfd. by Daikin
Industries, Ltd.). The fluorine-containing resin component
contained is FEP. In the fluorine-containing rubber latex
(GLS213F), the filler in each of amounts indicated in Table 4 and a
curing agent ("GL200B", mfd. by Daikin Industries, Ltd.) are mixed
to prepare a coating liquid. The coating liquid is spray-coated on
the fixing roller surface and is dried, followed by heating and
baking at 300.degree. C. for 15 minutes in an electric oven to
obtain the fixing roller. In Embodiments IV-1 and IV-2, the rounded
alumina filler of 10 .mu.m in particle size was added in the
addition amounts of 40 wt. % and 60 wt. %, respectively. In
Embodiments IV-3, the rounded alumina filler of 30 .mu.m in
particle size was added in the addition amount of 30 wt. %.
The results are show in Table 4.
TABLE-US-00004 TABLE 4 EMB. TH*.sup.2 FI*.sup.3 AA*.sup.4 Torque
CF*.sup.5 PP*.sup.7 NO.*.sup.1 Base (.mu.m) (.mu.m) (wt. %) (kgf
cm) (kgf) (%) E II-3 PFA 10 8 30 0.8 0.5 14.0 E II-4 PFA 10 15 30
1.0 0.6 11.0 E IV-1 GLS 20 10 40 0.9 0.9 16.0 E II-2 GLS 20 10 60
0.9 1.0 18.0 CE 10 GLS 20 10 70 UM*.sup.6 UM*.sup.6 -- E IV-3 GLS
20 30 30 0.9 1.1 15.5 *.sup.1"CE" represents Comparative Embodiment
and "E" represents Embodiment. *.sup.2"TH" represents the film
thickness. *.sup.3"FI" represents the rounded alumina filler having
the indicated average particle size. *.sup.4"AA" represents the
addition amount. *.sup.5"CF" represents the conveying force.
*.sup.6"UM" represents that the data is unmeasurable due to crack
of the coating and a poor film forming property. *.sup.7"PP"
represents the projection proportion.
As is apparent from Table 4, when the fluorine-containing rubber
latex coating is used, it becomes possible to further improve the
recording material conveying force while maintaining the torque
suppressing effect. This may attributable to the increase in
occupied ratio of the projections of the filler 18 protruded from
the surface layer 14 since the filler addition amount can be
increased by the use of the latex coating as in Embodiment IV-1.
Further, even when the addition amount of the filler 18 was
increased up to 60 wt. % (Embodiment IV-2), a good surface layer
was obtained without generating the crack or the like of the
coating. When the filler addition amount is increased up to 70 wt.
% as in Comparative Embodiment 10, the film forming property is
impaired and therefore about 60 wt. % is the (upper) limit as the
addition amount of the filler 18 which can be added.
Further, as in Embodiment IV-3, the fluorine-containing rubber
latex coating can be applied in a large thickness up to 20 .mu.m
and therefore the filler 18 having a larger particle size (30
.mu.m) can be used. As a result, the amount of protrusion of the
filler 18 protruded from the surface layer 14 becomes large to
enhance the recording material surface anchoring effect, so that it
would be considered that the recording material can be conveyed
further stably. Further, even in the case where the
fluorine-containing rubber latex coating was used, with respect to
the filler 18 having the particle size of less than 3 .mu.m, it was
unable to obtain the sufficient recording material conveying force.
Further, in the case where the rounded alumina filler 18 of 40
.mu.m in particle size was added with respect to the film thickness
of 20 .mu.m, the torque suppression and the recording material
conveyance could be compatibly realized but in the case where the
filler having the particle size more than 40 .mu.m was added, the
problem of the separation of the filler during the use occurred.
Therefore, even when the type and thickness of the base material
are changed, an applicable filler particle size is 3 .mu.m (lower
limit) or more and 200% (upper limit) or less of the film
thickness. Further, in comparison in Table 4, the rounded filler 18
of the pulverization type is used but as described in Embodiment 1,
when the different-shaped filler such as those of the nonspherical
shape including the flake-like, the needle-like, the rectangular,
the cubic, or the like shape, further improvement in conveying
force can be expected.
The optimum addition amount of the filler 18 is determined from the
preparation condition in this embodiment and therefore should be
appropriately adjusted in the case where the film forming property
is changed by changing the material used, the preparation condition
of the coating liquid or the baking condition. That is, the filler
addition amount is adjusted so as to be 10 wt. % or more and 60 wt.
% or less in the case where the total solid is 100 wt. % and is
also adjusted depending on the film thickness of the surface layer
14 and the average particle size of the filler 18.
Embodiment 3
In Embodiment 1 and Embodiment 2, a single species of the filler is
added in the surface layer 14 but this embodiment is characterized
in that two or more species of different fillers are added into the
base material for the surface layer 14. In this embodiment, a
constitution in which the fluorine-containing rubber latex coating
is used as the base material will be described.
As described in Embodiment 2, in the constitution in which the
fluorine-containing rubber latex coating is used as the base
material, the coating can be coated in a large thickness. For that
reason, by adding a filler 18 (one of the plural species of
fillers) having a larger particle size (average particle size), it
becomes possible to improve the recording material conveying force.
However, when the addition amount of the filler 18 having the
larger particle size is excessively large, the surface property of
the roller 10 becomes coarse, so that the adhesiveness to the
recording material is lowered. For that reason, the parting
property itself is impaired, so that problems of a lowering in
fixing property of the toner on the recording material, a lowering
in level of offset and accumulation of the offset toner are caused
to occur. In order to improve the surface property, it is possible
to decrease the addition amount while sacrificing the conveying
force but when the addition amount of the filler 18 having the
larger particle size is decreased, an area in which there is no
filler and the surface proper is good is increased. As a result,
the degree of close contact between the pad 20 and the roller 10
surface is increased to result in the torque increase.
Therefore, in this embodiment, a smaller particle size filler is
added while decreasing the addition amount of the larger particle
size filler. As a result, as shown in (a) of FIG. 7, also in the
area in which the larger particle size filler is not present, the
smaller particle size filler is surface-exposed, so that the
recording material conveying force can be maintained while
suppressing the torque increase and it is possible to suppress the
surface property of the flat surface portion at a level at which
offset or the like does not occur.
V: Comparison Regarding Addition of Two or More Species of
Fillers
The effect in the case where two species of fillers different in
particle size and shape were added was compared. In Embodiment V-1,
a flake-like alumina filler of 30 .mu.m in particle size (major
axis) was added as the larger diameter filler in the addition
amount of 15 wt. % and a rounded alumina filler of 4 .mu.m in
particle size was added as the smaller diameter filler in the
addition amount of 20 wt. %. That is, the filler 18 is constituted
by the plural species of fillers. Of these fillers one filler has
the average particle size larger than that of the other filler.
Further, in Embodiment V-II, a cubic silicon carbide (SiC) filler
of 15 .mu.m in particle size (major axis) was added as the larger
diameter filler in the addition amount of 15 wt. % and a rounded
alumina filler of 4 .mu.m in particle size was added as the smaller
diameter filler in the addition amount of 25 wt. %. That is, the
filler 18 is constituted by the plural species of fillers. Of these
fillers, at least one species of fillers has the nonspherical shape
such as the flake-like shape, the needle-like shape, the
rectangular shape, the cubic shape or the like shape. The base
material for the surface layer 14 is "GLS213F" similarly as in
Embodiment 2, and the coating film thickness is also 20 .mu.m. The
results are shown in Table 5.
TABLE-US-00005 TABLE 5 EMB. FI*.sup.2 AA*.sup.3 Torque CF*.sup.4
NO.*.sup.1 (type) (wt. %) (kgf cm) (kgf) Offset E IV-2 A 30 0.9 1.0
.DELTA. CE 11 B 30 0.9 1.3 .DELTA. CE 12 B 15 1.7 1.0 .smallcircle.
EV-1 B 15 0.85 1.2 .smallcircle. C 20 EV-2 D 15 0.88 1.1
.smallcircle. C 25 *.sup.1"CE" represents Comparative Embodiment
and "E" represents Embodiment. *.sup.2"FI" represents the filler.
"A" is the rounded alumina filler of 30 .mu.m in particle size. "B"
is the flake-like alumina filler of 30 .mu.m in particle size. "C"
is the rounded alumina filler of 4 .mu.m in particle size. "D" is
the cubic SiC filler of 15 .mu.m in particle size. *.sup.3"AA"
represents the addition amount. *.sup.4"CF" represents the
conveying force.
In Table 5, the offset was evaluated at two levels. In the case
where the offset was observed on the toner image after the fixing
even when the amount thereof is slight, the level was ".DELTA.",
and in the case where the offset was not substantially observed by
eyes, the level was ".largecircle.". As represented by Embodiment
IV-2 and Comparative Embodiment 11, in the case where the single
filler having a relatively large particle size is added in a large
addition amount, the surface property becomes coarse and thus the
offset becomes conspicuous. When the addition amount is decreased,
as in Comparative Embodiment, the surface property is improved but
the smooth surface area is increased correspondingly to a decrease
in site in which the filler is present, with the result that the
frictional force becomes large and thus the torque is
increased.
On the other hand, as in Embodiments V-1 and V-2, by the addition
of the smaller diameter filler while decreasing the addition amount
of the larger diameter filler, it becomes possible to suppress the
torque while maintaining the necessary conveying force and to
suppress the roughness of the flat surface portion to a tolerable
level of the offset. That is, the larger diameter filler functions
as the filler for providing the stable conveying force, and the
smaller diameter filler has the function of suppressing the torque
and the lowering in surface property. Thus, by effectively using
the functions of the fillers different in types for different
purposes, it becomes possible to improve a necessary characteristic
as the roller.
Further, the filler of alumina or the like has a high heat
conduction property and therefore the smaller diameter filler
particles added among the larger diameter filler particles also
have the function of improving the heat conductivity of the surface
layer, thus being advantageous in that the control temperature at
which the toner on the recording material is fixed can be
lowered.
Incidentally, the combinations of the type, the particle size, the
shape and the like of the plural species of the fillers to be added
are not limited to the combination of the larger diameter filler
and the smaller diameter filler shown in Table 5. The combination
should be appropriately optimized depending on the characteristic
of the fixing device used, by using the particle size, the shape,
the material and the like of the filler 18 in combination. For the
purpose of improving the recording material conveying force and
torque varying due to the friction and improving the
characteristics such as the parting property, the heat conductivity
and the like depending on the surface property, the combination may
be optimized so as to improve the characteristic, compared with
that of the conventional constitution using the single filler, by
combining the plurality of fillers. Further, the
fluorine-containing resin as the base material is also not limited
to the fluorine-containing rubber latex coating but may also be the
fluorine-containing resin such as PFA or FES used in Embodiment
1.
Other Embodiments
(1) In the fixing device 6 in Embodiments 1 to 3, the heating means
15 for externally heating the roller 10 is not limited to the
plate-like heater 15 for heating the roller 10 in contact with the
outer surface of the roller 10. The heating means 15 may also be a
heat roller rotating in contact with the outer surface of the
roller 10 and may be a halogen lamp or an infrared heater provided
opposed to and in non-contact with the outer surface of the roller
10. Further, the layer constituting the roller 10 may be provided
with the energization heat generating resistor layer as the heating
means. It is also possible to employ a constitution in which the
layer constituting the roller 10 is provided with an
electromagnetic induction heat generating layer and an exciting
coil for generating AC magnetic flux acting on the heat generating
layer is provided outside or inside the roller 10.
(2) The heating method of the roller 10 is not limited to the
external heating method but may also be an internal heating method
as shown in (b) of FIG. 7. The fixing device shown in (b) of FIG. 7
has a constitution in which the core metal 11 of the roller 10 is
formed with a hollow member in which the heat source such as the
halogen heater is inserted as the heating means 15 to heat the
roller 10 from the inside of the roller 10. In this constitution,
on the peripheral surface of the hollow roller core metal member
11, the surface layer 14 is formed directly or via the elastic
layer with a predetermined thickness. Further, when the surface
layer 14 has the constitution as described in Embodiments 1 to 3,
it becomes possible to suppress the torque against the sliding with
the fixed type pressing member 20 and to provide the stable paper
(recording material) conveying force even during the passing of the
recording material P. In this internal heating method, when the
elastic layer 12 of the roller 10 is formed in an excessively large
thickness, the rising time of the roller 10 is increased and in
addition, it becomes impossible to efficiently transfer thermal
energy from the heating means 15 provided inside the roller 10.
Therefore, the elastic layer 12 is not provided or is formed in a
small thickness as thin as possible. In this case, when the
pressing member 20 is a rigid member, it becomes difficult to form
the nip N necessary for the fixing. For that reason, the
constitution of the pressing member (pressing pad) 20 is, e.g.,
such that the parting layer 22 of PFA, PTFE or the like is provided
on the elastic layer 23 formed with the heat resistant rubber such
as the silicone rubber on the base material 21 to facilitate
formation of the nip N with the predetermined width. The
temperature control of the roller 10 is effected in the following
manner. The surface temperature of the roller 10 internally heated
by heat generation of the heat source 15 supplied with electric
energy from an AC power source 111 is detected by a temperature
detecting means 17 such as a thermistor or the like provided in
contact or non-contact with the surface of the roller 10. The
detected temperature information is inputted into the temperature
controller 109. The temperature controller 109 controls the
energization driving means 110 on the basis of the detected
temperature information. That is, by controlling the power supplied
from the heating means 15 to the heat source 15, the surface
temperature of the roller 10 is controlled at a predetermined
fixing temperature. In addition to the heating constitution of the
roller 10, it is also possible to appropriately employ other
constitutions such as an electromagnetic induction heating
constitution and a constitution in which the energization heat
generating resistor layer is formed on the roller itself by
lamination.
(3) The rotatable image heating member 10 is not limited to the
roller but may also be a flexible endless belt. FIG. 8 is a
schematic view showing an example of the external heating type
fixing device 6 in which the flexible endless belt is used as the
rotatable image heating member 10. The flexible endless belt 10 as
the rotatable image heating member is a lamination belt including,
from the inside to the outside, a flexible substrate layer 11, a
low heat conductive layer (elastic layer) 12, a high heat
conductive layer (elastic layer) 13 and a surface layer (parting
layer) 14 and has flexibility as a whole. The belt 10 is extended
and stretched between a driving roller 81 and a tension roller 82
and is rotationally driven by the roller 81 in the clockwise
direction indicated by an arrow. Further, at the belt contact
portion of the roller 81, a fixed non-rotational pressing member
(pressing pad) 20 for nip-conveying the recording material P in
press-contact with the outer surface of the belt 10 is provided.
The outer surface of the belt 10 is externally heated to a
predetermined image heating temperature by the halogen lamp 15 as
the heating means provided opposed to and in non-contact with the
outer surface of the belt 10. Further, when the surface layer 14 of
the belt 10 has the constitution as described in Embodiments 1 to
3, the torque can be suppressed against the sliding with the fixed
type pressing member 20 and the stable conveying force can be
provided even during the passing of the recording material P. The
temperature T control of the belt 10 is effected in the following
manner. The surface temperature of the belt 10 externally heated by
heat generation of the lamp 15 supplied with electric energy from
an AC power source 111 is detected by a temperature detecting means
17 such as a thermistor or the like provided in contact or
non-contact with the surface of the belt 10. The detected
temperature information is inputted into the temperature controller
109. The temperature controller 109 controls the energization
driving means 110 on the basis of the detected temperature
information. That is, by controlling the power supplied from the
power source 111 to the lamp 15, the surface temperature of the
belt 10 is controlled at a predetermined fixing temperature. In
addition to the heating constitution of the belt 10, it is also
possible to appropriately employ other constitutions such as an
electromagnetic induction heating constitution and a constitution
in which the energization heat generating resistor layer is formed
on the belt itself by lamination.
(4) The fixed type pressing member 10 is not limited to the
pressing pad but may also be a pressing sheet or a sheet-like
pressing member.
While the invention has been described with reference to the
structures disclosed herein, it is not confined to the details set
forth and this application is intended to cover such modifications
or changes as may come within the purpose of the improvements or
the scope of the following claims.
This application claims priority from Japanese Patent Application
No. 169159/2010 filed Jul. 28, 2010 which is hereby incorporated by
reference.
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